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Design and Construction of the First Commercial Cheng Cycle Series 7 Cogeneration Plant

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Design and Construction of the First Commercial Cheng Cycle Series 7 Cogeneration Plant THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47 St., New York, N.Y. 10017 The Society shall not be responsible for statements of opinions advanced in papers or in dis- cussion at meetings of the Society or of its Divisions or Sections, or printed in its publications. Discussion is printed only if the paper is published in an ASME Journal Papers are available from ASME for fifteen months after the meeting. Printed in USA. Design and Construction of the First Commercial Cheng Cycle Series 7 Cogeneration Plant J. LLOYO JONES, DR. CHUNG-NAN CHANG, DR. RAMARAO V. DIGUMARTHI, DR. WILLIAM M. CONLON International Power Technology Palo Alto, Calif. ABSTRACT on the Cheng Cycle. The HRSG unit consists of: A description is given of the Cheng Cycle Engine a superheater, located immediately downstream of and its application to cogeneration based upon the the turbine exhaust diffuser section, to raise first commercial plant. The paper covers a description the temperature of the injection steam to as high of the plant and its components, unique design features, a value as possible before injection. This the automatic control system and the plant operational temperature elevation reduces the amount of features. Initial operating performance and NOx additional fuel that needs to be supplied to the emission characteristics are cited. gas turbine to raise the temperature of the steam to turbine inlet temperature, and thus enhances INTRODUCTION the engine heat rate. The Cheng Cycle Series 7 Engine represents an a secondary combustor, located immediately down- innovative new concept in industrial gas turbines. A stream of the superheater, followed by a combustion detailed discussion of the Cheng Cycle, the potential duct section. This secondary combustion provides gains in power and efficiency that its application for the production of additional steam either would yield for a number of gas turbine engines, and for increased power generation or for process, an example of the performance improvements it offers depending upon the desired operating condition. in cogeneration applications is given in Reference 1. Three units were installed in two cogeneration an evaporator, located immediately downstream of plants by International Power Technology, Inc. in the combustion duct, for steam generation. 1984. Both plants completed acceptance tests in December 1984, and were in commercial operation in an economizer, located downstream of the steam January, 1985. Two units comprise a single plant generator, and at Sunkist Growers, Inc., in Ontario, California. The third unit, the first to be placed in operation, a feedwater heater. is located at the California State University at San Jose. This paper describes briefly the Cheng The operating regime of the Cheng Cycle Series 7 Engine Cycle Engine concept and characteristics and the Cogeneration application is illustrated in Fig. 2. San Jose State University cogeneration plant compo- Point 2 indicates the power generated by the basic nents, design features, operation and control system gas turbine driving the generator with no steam characteristics and initial performance levels. injection, and the amount of steam for process generated by the HRSG with no heat added to the exhaust gas by THE CHENG CYCLE SERIES 7 ENGINE COGENERATION SYSTEM the secondary combustor. Under this condition, the superheater operates dry. As steam is directed from An illustration of the Cheng Cycle Series 7 process to the gas turbine, the power output of the Engine in a cogeneration plant installation is given turbine and of the generator increases along line 2-1, in Fig. 1. The Cheng Cycle Series 7 Engine consists which represents a constant turbine inlet temperature of an Allison 501-KH gas turbine in combination with of 1895 degF (1308 degK) the highest allowable firing a heat recovery steam generator (HRSG) that is closely temperature for continuous duty. At point 1 all of matched to assure high cycle efficiency. Steam from the steam generated by the gas turbine exhaust heat the HRSG is injected into the gas turbine combustion energy is injected into the gas turbine and none is region to increase the power output of the basic available for process. Use of the secondary combustor engine. The KH version of the 501 engine incorporates expands the operating regime of the cogeneration system modifications by Allison specifically for operation from line 1-2 to include the entire area A . Line 3-4 Presented at the 1985 Beijing International Gas Turbine Symposium and Exposition Beijing, People’s Republic of China — September 1-7, 1985 STEAM TO ‘PROCESS - GENERATING SET 4 HEAT RECOVERY STEAM GENERATOR CHENG CYCLE SERIES 7-COGEN PLANT LAYOUT Fig. 1 by derating the gas turbine operation to lower turbine inlet temperatures. In the first commercial installa- tion at the California State University in San Jose, initial operation is being limited to a turbine inlet temperature of 1800 degF (1255 degK and a secondary combustion firing rate to provide a temperature of 1400 degF (1033 degK) entering the evaporator. The operating regimes for this plant are defined by the dotted lines in Fig. 2. THE FIRST COMMERCIAL PLANT The first commercial plant completed its formal acceptance tests in December, 1984. The plant is an indoor installation located in a previously unused TURBINE DERATING & | section of the existing power house at the University SECONDARY COMBUSTION | that had originally been planned for expansion of | the existing plant. A sectional elevation view of the | plant is given in Fig. 3, where it may be seen that | , , | | I. | | | | | major components are on a ground level operating floor, 0 1.0 20 3.0 40 with auxiliary equipment in a basement. The primary PROCESS THERMAL OUTPUT fuel is natural gas, which is supplied by the local MILLION Btu/Hour utility at a pressure of 100 to 150 psig. A rotary type gas compressor boosts the pressure to 300+ psig CHENG CYCLE SERIES 7-COGEN required to supply the gas turbine. The liquid fuel OPERATING REGIME is pumped from underground tanks to an elevated head tank from which it is drawn by a shaft driven fuel Fig. 2 pump on the gas turbine. Engine air is drawn from above through ducting into a plenum within the gas turbine-generator set enclosure. The ducting extends represents firing of the secondary combustor to obtain down to the basement level and outside to an open a temperature of 1600 degF (1144 degK entering the subsurface areaway. A self-cleaning filter and an evaporator. evaporative cooler through which the engine air is In most cogeneration installations, the process drawn are located in this areaway. Cooling air for steam demand is given highest priority. for example, If the generator, gearbox and gas turbine is drawn into the process steam demand were 20 million BTU/hour, the enclosure through a silencer/filter on top of the the electrical power output would be limited to about enclosure, circulated separately through the generator 4 megawatts. If a higher power output were required, and through the remainder of the enclosure and exhausted firing of the secondary combustor would provide through two ducts extending through the roof. additional steam for injection into the gas turbine Plan views of both the operating floor level and to permit the electrical power to be raised to any the basement level are shown in Figs. 4 and 5. The level up to the maximum of 6 megawatts, while maintain- engine inlet air ducting extension may be seen in these ing the process steam flow of 20 million BTU/hour. Figures and the filter and cooler units may be seen in Alternately, if the process steam demand increased, Fig. 5. The rather abrupt expansion duct section firing of the secondary combustor would permit the joining the gas turbine exhaust nozzle covering to the generation of more steam for process, while maintaining superheater is of internally insulated double wall the electrical power output of 4 megawatts. Obviously construction and is fitted with a series of turning combinations exist to permit operation anywhere within vanes to avoid flow separation and maintain the pressure the area A. Operation in areas B and C are possible 2 Fig. 3 ELEVATION VIEW, COGENERATION PLANT PLAN VIEW, COGENERATION PLANT, OPERATING FLOOR LEVEL. Fig. 5 PLAN VIEW, COGENERATION PLANT, BASEMENT LEVEL. drop of the exhaust gas/steam mixture at the lowest boilers will be placed on standby and used to provide practical value. Photographs taken during the final steam during periods when the cogeneration plant is construction stages and showing the generator set down for maintenance or overhaul. enclosure and HRSG are presented in Figs. 6 and 7. Electrical power is generated at 12.47 KV, the While the gas turbine generator set and the HRSG were voltage of the main electrical bus, and the generator designed to keep the external noise levels to within is tied through a protective breaker directly to the acceptable values, the plant control room is sound bus. Electrical energy is supplied to serve the proofed and air conditioned. Interconnecting power University needs, and excess is exported to the local and instrumentation wiring from the generator set, utility (Pacific Gas and Electric Company) grid. If the HRSG and auxiliary equipment is run in trays the University electric demand exceeds the output of beneath the operating floor, leaving a relatively the cogeneration plant, the shortfall can be imported free and uncluttered area around the unit. Cooling from the utility grid. In case the utility grid is fans for the compressed natural gas and for the down, the cogeneration plant can supply the University generator, gear box and gas turbine lubricating oil as an isolated grid. draw air through heat exchanger units and exhaust The cogeneration plant was installed at no cost into an open cooling tower area.
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